1. Field
The disclosed concept pertains generally to power circuits and, more particularly, to arc flash reduction systems for such power circuits.
2. Background Information
Arc flash reduction systems are starting to be widely used. Some systems have the trip unit of a circuit breaker measure the fault current and try to trip the circuit breaker as fast as possible. This clears the fault and reduces the arc flash, but the speed of tripping is typically in the order of about 50 mS.
Some arc flash reduction systems use devices to detect light from an arc flash and a shunt trip device on a circuit breaker to open the circuit breaker and clear the fault.
Some systems use both light and measured current from external devices to detect the fault and then trip the circuit breaker using the shunt trip device on the circuit breaker.
Some relatively very expensive systems use both light and measured current from external devices to detect the fault and then initiate a mechanism to create a short across a three-phase bus to prevent any current from flowing downstream to the area of the fault. This controlled fault is then used to force a protective fault trip on an upstream circuit breaker.
U.S. Patent Application Publication No. 2010/0214724 discloses a power switch disposed in a housing including a contact breaker configured to connect and disconnect a low-voltage switchgear from a power source supplying the low-voltage switchgear. A triggering device is configured to disconnect the low-voltage switchgear in an overload event. A first evaluation device is configured to evaluate an accidental arc overcurrent, and a second evaluation device is configured to evaluate the accidental arc overcurrent. The power switch is configured to be activated via an overcurrent signal generated by an arc monitoring system in response to the accidental arc overcurrent. The overcurrent signal is linked to at least one triggering signal. The second evaluation device has a threshold above a threshold of the first evaluation device. The triggering device is configured to be activated via a turn-off pulse when a signal from a current detection device is above the threshold of the second evaluation device.
There is room for improvement in arc flash reduction systems.